1. Field of the Invention
This invention relates to methods of and apparatus for coupling one fiber to another fiber, and, in particular, to such fibers as are used in fiber-optical communications systems. Accordingly, it is a general object of this invention to provide new and improved methods and apparatus of such character.
2. Description of the Prior Art
Optical fibers are useful in communication systems. They are also suitable in systems analogous to electric systems, such as control systems, burglar alarms, and the like. A coupler, useful for connecting optical fibers together, would be useful in fields analogous to that of electric wire connectors or couplers.
To implement practical fiber-optical communication systems, it is desirable to have fiber-to-fiber couplers which can be easily uncoupled and recoupled for the following system elements:
(a) Terminal connections--to connect the system fibers to a light source, detector, or repeater modules. Most modules would contain a short length of fiber terminated by a connector (which would form part of the module) which, in turn, would be coupled to the connector terminating the system fiber.
(b) Interchangeable fiber-to-fiber routing interconnections.
A fiber-to-fiber coupling method appropriate for the foregoing, and having properties of convenient operation, ruggedness and high coupling efficiency is an eccentric coupler discussed by S. Zemon, D. Fellows, and P. Sturk, "Eccentric Coupler for Optical Fibers: A Simplified Version," Appl. Opt. 14, 815 (1975). Such coupler is useful for coupling single-mode fibers (as well as multimode fibers) together and to components such as integrated optical circuits. However, the tuning operation of such coupler to achieve maximum throughput involves twisting of the fibers being coupled (Case b above), or the twisting of one fiber and of the terminal module (Case a above). This twisting can be through 180.degree. or more. Although this twisting is not a problem with long lengths of bare fiber in the laboratory, it becomes a problem when the fiber has protective jacketing (which increases the stiffness), especially if short lengths are involved as at a cable terminating point. Fibers are thereby subjected to stresses which can easily fracture the fiber, and it is hard to protect the fiber against this type of breakage. In addition, it may often be the case that the terminal module involves bulky electronics (such as cards) which would interfere with the twisting of the module. This particularly would be a problem in a closely-spaced multiple array of couplers.
One approach to solving the above problems is the technique of J. Guttman, O. Krumpholz, and E. Pfeiffer, disclosed in "Optical Fiber-Stripline Coupler," Appl. Opt. 14, 1225 (1975), in which one element to be coupled need not have any motion but the other (usually the fiber, in a fiber-module coupling situation) must be twisted in a double-eccentric arrangement. This approach, then, only solves half of the problem.
3. Prior Art Statement
As a means of complying with the duty of disclosure set forth at 37 CFR 1.56, applicants incorporate the following prior art statement in their specification. The statement shall serve as a representation that the prior art listed therein includes, in the opinion of the applicants and their attorney, the closest prior art (other than that appearing elsewhere in the specification) of which they are aware. This statement shall not be construed as a representation that a search has been made or that no better art exists.
The following United States patents may be of interest, copies of which accompany this application:
U.S. Pat. No. 3,800,388 to Borner et al. relates to apparatus for aligning two optical components along a common optical axis, utilizing two holders, each holding a respective one of the optical components at a fixed distance from the axis of rotation of the respective holder. The holders are rotated with respect to each other until the optical components become optically aligned. The optical components are firmly secured in place once they are aligned by temporarily heating the housing, soldering, welding, clamping, or gluing. Generally, the components are held in their respective holders, where practicable, by force fit; with very small diameter, for example about 100.mu., it is difficut to form a bore with a corresponding inner diameter in the guide pin for holding this component, hence, a larger diameter bore can be used in association with adhesive. Disadvantageously, rotating the holders would tend to rotate the optical components, causing twisting.
U.S. Pat. No. 3,871,744 to Bridger et al. discusses fiber to fiber coupling by eccentric mounting in plugs in the background portion in column 1, ines 26-38. Since the fibers are held in place by the plugs, rotation of the plugs would cause the fibers to twist.
U.S. Pat. No. 3,902,784 to Dakss et al. relates to apparatus for forming an optical fiber connector. The optical fiber connector main body fixture includes means for positioning an optical fiber connector main body therein in a predetermined manner relative to the axis and thereafter holding the optical fiber connector main body in that position. In the case where the optical fiber connector main body is of a right cylindrical form, the preferred arrangement is a V-shaped mounting groove having planar vertically oriented side surfaces. A retainer such as a nylon tipped screw may be used to hold an optical fiber connector main body against the surfaces. A similar means is associated with the optical fiber fixture.
U.S. Pat. No. 3,914,880 to Dakss et al. relates to an optical fiber coupler and connector which illustrates a V-shaped holder arrangement.
U.S. Pat. No. 3,936,142 to Kersten discusses, in the background portion, that fibers can be held eccentrically in pins which are in turn eccentrically guided in bushings. By rotating the pins in relation to one another, optimum coupling of the fiber ends can be manually effected.
U.S. Pat. No. 3,936,143 to Sato discloses eccentric relationship with a means to turn only one fiber for adjustment.
U.S. Pat. No. 3,938,895 to Bridger et al. relates to a method of positioning an optical fiber which utilizes a V-shaped holder.
U.S. Pat. No. 3,999,841 to Dakss et al, which relates to a method for forming an optical fiber connector, also discloses a means for positioning an optical fiber with a V-shaped holder.
U.S. Pat. No. 4,019,806 to Fellows et al. discloses a holder for eccentrically mounted fibers. Rotation of an optical connector would cause twisting of the optical fiber, which may cause distortion and other undesirable effects.
U.S. Pat. No. 4,030,809 to Onishi et al. relates to an optical connector which is included of interest for eccentric cam mounting.
Broadly, the prior art teaches either concentric coupling (unrelated to the teachings of this invention) or eccentric coupling where optical fibers are frictionally held, causing twisting of the fiber upon rotation of the connector.
Another publication of the prior art, of interest, is an article, "Optical Fiber-Stripline-Coupler," J. Guttmann et al., Appl. Opt., May 1975, Vol. 14, No. 5, pp. 1225-7. Its relevance was discussed above (see section 2).